1. Field of the Invention
The present invention relates generally to cabinets supported on casters and, more particularly to an arrangement for casters on cabinets for use on access or raised floors of a computer room or the like.
2. Relation to Prior Art
As the computer and communication needs of business increase, computer or equipment rooms require flexibility and wire management. These rooms must allow for repair, rearrangement and upgrading of computer equipment and services. Increased data processing needs for the conventional office have been an increasing trend for businesses. Companies are anxious to create office environments that can be readily reconfigured with as little interference as possible to the fixed structure of the building. Many techniques exist for dealing with the large amounts of wiring required for computer and equipment rooms for the modem office. One such technique uses access flooring.
FIG. 1 illustrates an isometric view of an equipment cabinet 10 supported on a access floor 20 by a plurality of casters 12. The equipment cabinet may include computer or telecommunications devices or other equipment required to support such devices. A structural system of interchangeable floor panels 22 create access floor 20. Columns 24 support panels 22 at a specified height above raw floor 26 of the building. There are many types of access floors and panels, including welded steel panels having hollow or filled core. Most access floors are made of steel or aluminum.
Columns 24 vary in height typically from 6 to 30 inches. Several systems may be used to support or sustain the panels on the columns. For example, the panels may be held on the columns by gravity, snaps, bolts or locks. In addition, stringers or bars that run from column to column in the grid may provide additional support.
Access panels 22 create a plenum 28 below access floor 20. Wiring (not shown) may be distributed in plenum 28 between raw floor 26 and access floor 20. By removing interchangeable panels 21, one can access the wiring contained within plenum 28. In plenum 28, the electrical wiring can be economically installed. The plenum can also be used to deliver conditioned air.
To properly accommodate and handle heavy equipment and loads, the access floor and panels are built to various weight and strength specifications. The floors must be able to handle static loads and rolling loads. Equipment having common commercial casters for support and rolling can deform the access floor system or even cause the flooring to fail.
For example, Table I below illustrates criteria for an access floor system using steel panels held by gravity and stringers. The floor panel can support a concentrated load of 1000 lbs. and an ultimate load of 2100 lbs. The rolling loads allowable for a minimum deformation (0.040 inches) of the panels is about 400 lbs. for up to 10,000 passes. The values presented are for a commercial access floor as provided by the xe2x80x9cAll Steel 1000 Systemxe2x80x9d from Tate Access Floors, Inc.
FIGS. 2A-B illustrate prior art caster arrangements. A portion of access floor 30 is shown from above. Three rows 32, 34, 36 of access panels and three columns A, B, C create the grid of the present portion of access floor 30. The panels are typically square and have a side length of one or two feet. The panels are arranged in a grid as shown. An outline of a cabinet 40 lies within the portion of access floor 30 and represents the location of an equipment cabinet 40 on the floor. Cabinet 40 has a plurality of casters 41-49 arranged under the cabinet to provide support and rolling of the cabinet on access floor 30.
For the present discussion, example dimensions and values will be used to illustrate and describe the arrangement of casters and loads for FIG. 2A. The access panels that compose access floor have a side length of 24 inches and have performance criteria as shown in Table 1. Cabinet 40 has a width W of 54xe2x80x3 and a depth D of 33xe2x80x3. Assuming that cabinet 40 holds equipment that creates a uniform load weighing 4500 lbs., each of the casters 41-49 supports a weight of 500 lbs.
From Table 1, each panel of access floor 40 can sustain a recommended concentrated load of 1000 lbs. and an ultimate load of 2100 lbs. With the arrangement of the nine casters 41-49 to support cabinet 40 of 54xe2x80x3xc3x9733xe2x80x3, the weight can be properly distributed to the various panels as the cabinet rests or rolls on access floor 30. For instance, panel 34A supports weight of cabinet 40 through casters 41 and 44. If each caster 41 and 44 applies a concentrated load of 500 lbs. each, then the panel 34A supports an ultimate load of 1000 lbs. and falls within the performance criteria of Table 1. In particular, the concentrated load, i.e., the point load from a single caster, applied to panel 34A does not exceed the 1000 lbs. limit. Also, the combined static load of casters 41 and 44 being 1000 lbs. does not exceed the ultimate load of the panel of 2100 lbs. in Table 1.
Similarly, panel 34B supports casters 42 and 45 having 1000 lbs. of static load, and panel 34C supports casters 43 and 46 having 1000 lbs. of static load. Furthermore, panels 36A, 36B and 36C each support a single caster having static loads of 500 lbs. In this arrangement then, the casters properly distribute weight of the cabinet to the panels of the access floor. Importantly, no matter how the cabinet is ultimately situated on the access floor differently than depicted in FIG. 2A, a given panel will support at most only the static load of two casters.
FIG. 2B shows another caster arrangement according to the prior art. Cabinet 50 has similar dimensions as the cabinet described in FIG. 2A. Specifically, width W is 54 inches, and depth D is 33 inches. Six casters 51-56 support cabinet 50. If the cabinet uniformly weighs 4500 lbs. as before, each caster applies a concentrated load of 750 lbs. on a panel of access floor 30. With the present arrangement of six casters 51-56 for cabinet 50 on access floor 30, each panel supports the load of only one caster for any given orientation or roll of the cabinet.
Given the panel side length of 24 inches and the performance criteria of Table 1, access floor 30 in FIGS. 2A and 2B can properly accommodate a 4500 lbs. cabinet having the dimensions of 54xe2x80x3 width and 33xe2x80x3 depth and nine or six casters distributed uniformly below the cabinet. With the present trends, the computer and telecommunications industries design electrical components smaller and more compact. More equipment is being used by businesses and placed in more restrictive environments and computer rooms. These trends develop a growing need for more compact cabinets for containing a significant amount of equipment. Present caster arrangements if used with smaller cabinets results in problems and failures with respect to the access floor systems used in many data centers and computer rooms. For this reason, a need exists for a caster arrangement for more compact and densely equipped cabinets that will not overburden access floor systems.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In view of the foregoing and other considerations, the present invention relates to an arrangement for casters on cabinets having electronic equipment for use on access or raised floors of a computer room or the like.
In accordance with one aspect of the present invention, there is provided a method for arranging casters to support a cabinet on an access floor. The access floor has a plurality of panels having a side length S. The cabinet is a right quadrangle having side lengths of W and D. The method includes establishing four corner casters on the corners of the right quadrangle. The method includes establishing a plurality of casters along sides W of the cabinet by spacing the plurality of casters at a distance of approximately       (          214      240        )    ⁢  S
from one another. The method includes establishing a plurality of casters along sides D of the cabinet by spacing the plurality of casters a distance of at least             2        ⁢    S    -            (              214        240            )        ⁢    S  
form one another. Maintaining each of the casters a minimum distance from the sides of the right quadrangle cabinet to which the casters lie adjacent ensures the stability of the cabinet. The sides W are each at least twice the distance                     2            ⁢      S        -                  (                  214          240                )            ⁢      S        ,
and the sides D are each at least twice the distance       (          214      240        )    ⁢      S    .  